Stephen Cohen, a longtime lawyer at the U.S. Securities and Exchange Commission, has joined Sidley Austin as a securities and derivatives enforcement and regulatory partner in Washington, D.C. The move comes eight months after Cohen left the SEC after nearly a dozen years at the securities regulator.

“Twelve years is a fair amount of anyone’s lifetime and I had an exceptionally talented team [at the SEC],” said Cohen on Monday. “I was just ready for a new challenge.”